Self-Explanatory Protocol Buffer Lang Guide (CheatSheet)

LearnXInYMinProtocolBuffer.proto

/*
* Self-Explanatory Protocol Buffer Lang Guide
*/


/*
* Why Protocol Buffers?
* Protocol buffers are Google's language-neutral, platform-neutral, extensible mechanism for serializing structured data – think XML, but smaller, faster, and simpler.
* You define how you want your data to be structured once, then you can use special generated source code to easily write and read your structured data to and from a variety of data streams and using a variety of languages.
* Protocol Buffers are Schema Of Messages. They are language agnostic.
* They can be converted to binary and converted back to message formats using the code generated by the protoc compiler for various languages.
*/

/*
* Language Syntax
*/

/*
* Specifying Syntax Of Protocol Buffer Version
* Specifying Which Protocol Buffer Version To Use
* It can be usually proto3 or proto2
*/
syntax = "proto3";

/*
* Declaring Message In Protocol Buffer:
* As you can see, each field in the message definition has a unique number.
* These field numbers are used to identify your fields in the message binary format,
* and should not be changed once your message type is in use.
* Note that field numbers in the range 1 through 15 take one byte to encode, including the field number and the field's type (you can find out more about this in Protocol Buffer Encoding).
* Field numbers in the range 16 through 2047 take two bytes. So you should reserve the numbers 1 through 15 for very frequently occurring message elements.
* Remember to leave some room for frequently occurring elements that might be added in the future.
* The smallest field number you can specify is 1, and the largest is 2^29 - 1, or 536,870,911.
* You also cannot use the numbers 19000 through 19999 (FieldDescriptor::kFirstReservedNumber through FieldDescriptor::kLastReservedNumber),
* as they are reserved for the Protocol Buffers implementation - the protocol buffer compiler will complain if you use one of these reserved numbers in your .proto.
* Similarly, you cannot use any previously reserved field numbers.
*
*/

/*
Syntax For Declaring Message:
    message ${MessageName} {
        ${Scalar Value Type} ${FieldName1} = ${Tag Number1};
                .
                .
                .
        ${Scalar Value Type} ${FieldNameN} = ${Tag NumberN};
    }

Default Values Will be applied any case if the message doesn't contain a existing field defined
in the message definition
*/

message MessageTypes {
    /*
    * Scalar Value Types
    */
    string stringType = 1; // A string must always contain UTF-8 encoded or 7-bit ASCII text. Default value = ""

    // Number Types, Default Value = 0
    int32 int32Type = 2; // Uses Variable Length Encoding. Inefficient For Negative Numbers, Instead Use sint32.
    int64 int64Type = 3; // Uses Variable Length Encoding. Inefficient For Negative Numbers, Instead Use sint64.
    uint32 uInt32Type = 4; // Uses Variable Length Encoding
    uint64 uInt64Type = 5; // Uses Variable Length Encoding
    sint32 sInt32Type = 6; // Uses Variable Length Encoding. They are efficient in encoding for negative numbers.
                           // Use this instead of int32 for negative numbers
    sint64 sInt64Type = 7; // Uses Variable Length Encoding. They are efficient in encoding for negative numbers.
    // Use this instead of int64 for negative numbers.

    fixed32 fixed32Type = 8; // Always four bytes. More efficient than uint32 if values are often greater than 2^28.
    fixed64 fixed64Type = 9; // Always eight bytes. More efficient than uint64 if values are often greater than 2^56

    sfixed32 sfixed32Type = 10; // Always four bytes.
    sfixed64 sfixed64Type = 11; // Always Eight bytes.

    bool boolType = 12; // Boolean Type. Default Value = false

    bytes bytesType = 13; // May contain any arbitrary sequence of bytes. Default Value = Empty Bytes

    double doubleType = 14;
    float floatType = 15;

    enum Week {
        UNDEFINED = 0; // Tag 0 is always used as default in case of enum
        SUNDAY = 1;
        MONDAY = 2;
        TUESDAY = 3;
        WEDNESDAY = 4;
        THURSDAY = 5;
        FRIDAY = 6;
        SATURDAY = 7;
    }
    Week wkDayType = 16;

    /*
    * Defining Collection Of Scalar Value Type
    * Syntax: repeated ${ScalarType} ${name} = TagValue
    */
    repeated string listOfString = 17; // List[String]
}

/*
* Defining Defined Message Types In Other Message Definition
*/
message Person {
    string fname = 1;
    string sname = 2;
}

message City {
    Person p = 1;
}

/*
* Nested Message Definitions
*/

message NestedMessages {
    message FirstLevelNestedMessage {
        string firstString = 1;
        message SecondLevelNestedMessage {
            string secondString = 2;
        }
    }
    FirstLevelNestedMessage msg = 1;
    FirstLevelNestedMessage.SecondLevelNestedMessage msg2 = 2;
}

/*
* Importing Message From A File
*/

// one.proto
// message One {
//     string oneMsg = 1;
// }

// two.proto
//  import "myproject/one.proto"
//  message Two {
//       string twoMsg = 2;
//  }


/*
* Advanced Topics
*/


/*
* Handling Message Type Changes:
* Never Change/Use The TagNumber Of A Message Field Which Was Removed
* We should use reserved in case of message definition update.
* (https://developers.google.com/protocol-buffers/docs/proto3#updating)
*/

/*
* Reserved Fields
* It's used in case if we need to add/remove new fields into message.
* Using Reserved Backward and Forward Compatibility Of Messages can be achieved
*/


message ReservedMessage {
    reserved 0, 1, 2, 3 to 10; // Set Of Tag Numbers Which Can't be reused.
    reserved "firstMsg", "secondMsg", "thirdMsg"; // Set Of Labels Which Can't Be reused.
}

/*
* Any
* The Any message type lets you use messages as embedded types without having their .proto definition.
* An Any contains an arbitrary serialized message as bytes,
* along with a URL that acts as a globally unique identifier for and resolves to that message's type.
* For Any to work we need to import it as shown below.
*/
/*
    import "google/protobuf/any.proto";
    message AnySampleMessage {
        repeated google.protobuf.Any.details = 1;
    }

*/


/*
*  OneOf
* There are cases, wherein only one field at-most might be present as part of the message.
* Note: OneOf messages can't be repeated.
*/

message OneOfMessage {
    oneof msg {
        string fname = 1;
        string sname = 2;
    };
}


/*
* Maps
* Map fields cannot be repeated.
* Ordering Of A Map Is Not Guaranteed.
*/

message MessageWithMaps {
    map<string, string> mapOfMessages = 1;
}


/*
* Packages
* Used for preventing name clashes between protocol message types
* Syntax:
    package ${packageName};

    To Access the package;
    ${packageName}.${messageName} = ${tagNumber};
*/

/*
* Services
* Message Types Defined For Using In RPC system.
*  When protoc compiler generates for various languages it generates stub methods for the services.
*/

message SearchRequest {
    string queryString = 1;
}

message SearchResponse {
    string queryResponse = 1;
}
service SearchService {
    rpc Search (SearchRequest) returns (SearchResponse);
}

/*
* Generating Classes In Various Languages For Protocol Buffers
*/

/*
* protoc --proto_path=IMPORT_PATH --cpp_out=DST_DIR --java_out=DST_DIR --python_out=DST_DIR --go_out=DST_DIR --ruby_out=DST_DIR --objc_out=DST_DIR --csharp_out=DST_DIR path/to/file.proto
*/



/*
* Information From: https://developers.google.com/protocol-buffers/docs/proto3
*/